The head of the U.S. military’s Special Operations Command said Wednesday that Air Force gunships, needed to provide close air support for American commandos and U.S.-backed rebel fighters in Syria, were being “jammed” by “adversaries.”

An Air Force AC-130 gunship was among the U.S. military aircraft used to kill dozens of Russian mercenaries in Syria in early February. The Pentagon said the mercenaries attacked an outpost manned by American commandos and U.S.-backed fighters of the Syrian Democratic Forces (SDF), comprising Syrian Kurdish and Arab fighters.